Product Overview

The Thermal Conductivity Flow Switch NK33EX-150 Series is designed based on the thermal conductivity principle for continuous monitoring of liquid and gas flow in industrial pipelines. The enclosed probe contains two resistors: one heated detection resistor and one reference resistor. When the medium flows, heat is transferred from the heated resistor, causing a resistance change. The controller compares the resistance difference to accurately determine the flow condition.

The sensing probe features a special anti-scaling coating, effectively reducing the adhesion of scale, rust, and other contaminants inside pipelines, resulting in improved anti-fouling performance and long-term operational stability.

The NK33EX-150 Series provides real-time flow monitoring without moving parts, making it suitable for demanding industrial environments where reliable flow protection is required.

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Why Choose the NK33EX-150 Flow Switch?

Selecting the right explosion-proof flow switch NK33EX-150 is essential for protecting pumps, pipelines, cooling systems, and industrial processes. The NK33EX-150 Series offers several practical advantages:

• Thermal measurement principle with no moving mechanical parts
• Anti-scaling probe coating for improved long-term stability
• Explosion-proof design (ExdII CT6) for hazardous environments
• IP67 protection suitable for harsh industrial conditions
• Adjustable switching points for different pipe diameters
• Digital flow percentage display for intuitive monitoring
• Optional relay, PNP, NPN, and integrated 4–20mA analog output
• Supports gas and liquid flow monitoring with maintenance-free operation

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Product Features

The NK33EX-150 Series is designed for reliable industrial flow monitoring with flexible installation and output options.

Key Features

• Thermal conductivity measurement technology
• Conical probe design minimizes material entanglement
• Anti-fouling coated sensing probe
• Fully waterproof housing with waterproof adjustment knob
• Parameter adjustment without removing sealing screws
• Suitable for various pipe diameters
• Adjustable switching point
• Optional corrosion-resistant probe materials
• Pressure resistance up to 100 Bar (customizable up to 40 MPa)
• Digital flow percentage display
• Optional Relay, PNP, NPN, and integrated 4–20mA analog output
• No moving parts and maintenance-free operation
• Fast installation and long service life

The flow switch can monitor:

• Medium flow rate
• Flow increase or decrease
• Presence or absence of medium
• Flowing or static conditions
• Pipeline flow interruption
• Pump dry-running protection

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Working Principle

The NK33EX-150 Series operates using the thermal conductivity principle.

Inside the sealed sensing probe are two resistors:

• One heated resistor acts as the sensing element.
• One unheated resistor serves as the reference element.

When no medium is flowing, the temperature difference between the two resistors remains stable.

As the medium begins to flow, heat generated by the sensing resistor is carried away. The resulting resistance change is continuously compared with the reference resistor. The controller calculates this difference to determine the flow condition and outputs switching or analog signals accordingly.

The anti-scaling probe coating minimizes contamination from scale, rust, and deposits, maintaining stable measurement performance over extended operation.

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Product Applications

The NK33EX-150 Series is suitable for continuous flow monitoring and equipment protection in industries including:

• Petrochemical plants
• Power generation
• Metallurgy
• Steel manufacturing
• Paper mills
• Food processing
• Water treatment
• Battery manufacturing
• Hydraulic systems
• Pneumatic systems
• Cooling water circulation
• Cutting fluid monitoring
• Lubricating oil systems
• Pump dry-run protection

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Typical Application Example

Pump Dry-Run Protection in an Industrial Cooling Water System

In industrial circulating cooling systems, insufficient water flow caused by clogged filters, pump failure, or pipeline blockage can quickly result in pump dry running and equipment overheating.

The NK33EX-150 Series is installed on the cooling water pipeline to continuously monitor flow conditions. When flow falls below the preset threshold, the switch immediately outputs an alarm or shutdown signal to the PLC, allowing the control system to stop the pump or activate backup equipment.

Its thermal sensing technology requires no moving mechanical parts, while the anti-scaling probe helps maintain stable operation in cooling water environments with suspended impurities or scale buildup.

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Technical Specifications

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Wiring Diagram

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Size Chart

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Button Setting Instructions

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Frequently Asked Questions (FAQ)

What media can the NK33EX-150 monitor?

The flow switch is suitable for water, oil, air, cutting fluids, lubricating oil, and other compatible gas or liquid media.

Is it suitable for hazardous environments?

Yes. The NK33EX-150 is rated ExdII CT6, making it suitable for explosion-proof industrial applications where certified equipment is required.

Does the sensor require regular maintenance?

No. The thermal measurement design has no moving parts, and the anti-scaling coated probe helps reduce contamination, minimizing maintenance requirements.

Can it be connected to PLC systems?

Yes. The device supports PNP, NPN, Relay (SPDT), and optional 4–20mA analog outputs, allowing straightforward integration with PLC and industrial control systems.

What protection does it provide?

The NK33EX-150 is commonly used for flow monitoring, flow interruption detection, cooling circuit monitoring, and pump dry-running protection in industrial systems.